A brake system of this type is, for example, known from European patent EP 0,706,466 B1. This known automatic brake system contains two sensors that are assigned to the gas pedal as well as a third sensor, wherein the output signals of all sensors are fed to an electronic control that automatically triggers the braking process. The first sensor which is assigned to the gas pedal and preferably realized in the form of a pressure sensor is arranged underneath the gas pedal. The second sensor delivers a signal when the foot of the driver is removed from the gas pedal. The third sensor is arranged between the gas pedal and the brake pedal and detects the movement of the driver's foot from the gas pedal toward the brake pedal. The disadvantages of this known brake system are the relatively high expenditure associated with the complex sensor arrangement as well as the risk of malfunctions, in particular, of the third sensor, e.g., due to soiling.
The present invention is based on the objective of disclosing an automatic brake system of the initially-mentioned type which makes it possible to shorten the stopping distance by means of propulsion-specific control signals of the motor vehicle, while simultaneously lowering the required costs. The functional reliability of the proposed brake system should be increased, and the scope of applications for said brake system should be broadened.
According to the invention, this objective is attained by providing means which ensure pre-filling of the wheel brakes when the sensor signal occurs. The term "pre-filling" which is conventionally used in brake engineering refers to an activation of the brake system that is connected in series with the wheel brakes, wherein the hydraulic pressure is increased in such a way that the brake linings merely adjoin the brake disk or brake drum while no deceleration of the motor vehicle takes place.
According to one embodiment of the invention, the control signal represents the load status of the motor vehicle engine or the motion of the gas pedal or the like which occurs when the actuating force is discontinued. It would also be conceivable to utilize the decrease in the engine speed as the control signal. However, this signal would be influenced by the inertia of masses of rotating and oscillating engine components, i.e., this signal would be more suitable as a fail-safe signal.
According to advantageous additional developments of the invention, the control signal may be generated by an electronic control device of a computer-controlled automatic transmission or represent a change in the pressure in the intake manifold of the engine or in the back pressure in the exhaust system. The engine vacuum is not subject to a significant delay threshold with respect to its response behavior, i.e., a sudden release of the gas pedal or the like can be rapidly and reliably detected, e.g., by means of a pressure switch.
According to another advantageous embodiment of the invention, it is proposed that the control signal be derived from performance characteristics stored in the electronic control device of a fuel injection system or from performance characteristics stored in the electronic control unit of an engine ignition system. In this case, particularly advantageous control signals are the fuel injection interrupt signal generated in motor vehicles with fuel cut-off in the overrun or a spark advance angle shift signal that, for example, can be used to realize "retarded ignition" during a sudden advance angle shift.
Naturally, the scope of the invention also allows additional embodiments, in which the control signal is triggered by a supercharger boost pressure sensor, a pressure sensor that preferably cooperates with the control unit of the engine ignition, or by a throttle sensor or switch that detects the adjustment of the throttle of the motor vehicle.
According to another alternative of the invention, it is proposed that the control signal be triggered by an idle switch that is assigned to a fuel injection pump.
According to one particularly advantageous additional development of the invention, the brake system be realized in the form of a hydraulic brake system, and the means for pre-filling the wheel brakes consist of a hydraulic pre-charging pump or a brake booster that can be controlled independently of the driver's intentions. In this case, the brake booster is preferably realized in the form of a vacuum brake booster, the control valve of which can be electromechanically actuated.
According to another advantageous characteristic of the invention, a second control signal is fed to the electronic control unit, wherein the second control signal is generated by a device for detecting when the foot or the hand of the driver come in contact with the brake pedal or the like, and wherein the pre-filling process is interrupted if no such signal occurs.
In this case, it is particularly advantageous if, according to another additional development of the invention, means are provided which measure the duration between the beginning of the pre-filling process and the reception of the second control signal, wherein the measured value is compared to a predetermined value.
In order to detect the driver's intentions with respect to an unintentional deceleration of the motor vehicle, the invention proposes to interrupt the pre-filling process if the predetermined value is exceeded.
In order to assist the driver, in particular, during so-called panic brake maneuvers, the invention proposes that full brake application take place if the predetermined value is not reached.
In this case, it is particularly advantageous if the electronic control unit is linked to an engine control device or to the electric switching circuits of an ABS/ARS control device. If the invention is correspondingly miniaturized, it can be integrated into the aforementioned control devices.
The invention is described in detail below with reference to one embodiment that is illustrated in the figures. In this respect, components that are not essential for the invention were omitted.